1. Field of Art
This invention relates to a packaging system and in particular to a three-piece closure assembly for sealing containers made of paperboard, plastic or a composite of paper and metal foil among other materials.
2. Brief Description of the Prior Art
Fibrous composite containers are used in packaging numerous products including solids, liquids and semi-liquids. Some composite containers include a paperboard layer and inside and/or outside layers of metal foil. The metal foil layers are impervious to the packaged items and to the ambient surroundings and protect the contents of the container and/or the paperboard layer. Other fibrous containers which are used for packaging dry goods may be made of paperboard having no protective foil.
A number of closure systems are known for closing fibrous containers. For example, U.S. Pat. No. 3,892,351 discloses a composite tubular container body having an outwardly rolled top rim with a foil membrane type closure sealingly secured to the rolled rim and a plastic overcap secured on the container over the foil membrane. The foil membrane is heated by induction currents to seal it to the rolled rim. U.S. Pat. No. 3,396,899 discloses another system for sealing a fibrous container in which a heat regenerating adhesive is applied as an annular band on the top edge of the container with a foil liner secured to such band and a protective closure over the foil liner. The protective closure may be secured on the container by a pressure sensitive tape around the periphery of the closure. Another example of a system for sealing fibrous containers is disclosed in U.S. Pat. No. 3,353,739 in which a metal easy-opening end is seamed on the end of a composite container.
Sealing of fibrous containers is difficult due to the lack of flexibility of fibrous material such as paperboard and the irregularity of the edges of such container to which a closure is to be sealed. Rolling or otherwise deforming the edges of a fibrous container tends to wrinkle and damage the edges and therefore produces an uneven and sometimes degraded surface to which a closure must be sealed.
Induction heat sealing of containers is well known as is disclosed in a number of patents including U.S. Pat. Nos. 3,815,314; 2,937,481; 2,620,939 and 3,460,310. Many induction heat sealing systems involve the use of a foil membrane or liner having a heat seal resin on one or both sides thereof to facilitate sealing or securing the membrane to the entrance mouth of a container and to an overcap over the foil liner. Additional prior disclosures of interest are contained in U.S. Pat. Nos. 2,964,208; 3,325,034 and 3,445,024 which disclose plastic sealing rings which are adapted to be secured on the entrance mouth of a container to facilitate sealing a closure on such a container.
The prior art is lacking in a simple and reliable system for sealing fibrous containers at high speeds.